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Aquarium.Net A Discussion of Algae

Sept. 1996 , Dr. Shimek talks about several different algae found frequently in reef tanks. Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

Slime, Goo, and Hair - A Discussion of Algae

by Ronald L. Shimek

In one way or another, one of the topics most on the minds of
reef aquarists is the control of algal populations in their systems. At the
same time algal organisms are amongst the least understood organisms that
inhabit most reef tanks. In large part this is probably due to the sheer
diversity of algae. The various types of algae that seem to most concern
aquarists are red slime algae, brown slime algae, diatoms, hair algae, coralline
algae, and the symbiotic zooxanthellae found in many tropical organisms.
Brown slime algae and zooxanthellae are similar in many regards and are closely
related. But all of the others belong to separate, very distinct groups with
little in common except photosynthesis.

So... What is an alga? (The singular of the word is alga, the plural is algae).
Commonly algae are considered to be all of the photosynthetic organisms growing
in water or water films that are not vascular plants. Vascular plants are
the plants we commonly see on land, flowering plants, conifers, ferns, and
few others. Vascular plant diversity is very low in the sea, only a few species
of grass, and possibly mangroves can be found growing in this environment.
While these are often very important ecologically, relatively few aquarists
bother trying to grow either sea grasses or mangroves. Virtually all other
photosynthetic organisms in marine ecosystems have been or are called algae.

Photosynthesis is the process by which light energy is used by organisms
to turn carbon dioxide and water into sugar. Light is captured by a molecule
of chlorophyll and with the use of an enzyme system the energy in the light
is used fuse carbon dioxide and water into glucose or another simple sugar.
Different methods of light capture and different kinds of chlorophyll
characterize the different kinds of algae. Nonetheless, they all have the
same basic requirements: light, water, and dissolved carbon dioxide gas.
Additionally they all use other organic and inorganic nutrients, such as
phosphate, nitrate, or sulfate to produce proteins and other chemicals. This
similarity of requirements is really at the root of the problem of algal
control. The basic question is, "How to limit growth of pest algae, while
maximizing the growth of beneficial algae?" One of the ways we can approach
the problem of control is by an examination of the various types of algae
in general way to see if there are unique controls for any of the algal groups.

Algal Diversity

The diversity of algae is truly amazing; algae can be found in two (and recent
evidence indicates maybe more) kingdoms of life. Red slime algae are essentially
photosynthetic bacteria or microbes and are placed in the kingdom Monera.
Traditionally the remaining algae have been placed in the plant kingdom,
but the more recent trend is to place them into the kingdom protista, a kingdom
containing mostly unicellular organisms. Finally, recent comparative examination
of the genetic material, DNA, indicates that a few groups, such as the red
algae and including coralline algae, may be sufficiently distinct to be
considered in their own kingdom.

CYANOBACTERIA
- the red (and sometimes green, blue-green, purple,
or black) slime algae. There are at least several dozen, and perhaps a few
hundred, species. The name literally means blue green algae, but most marine
forms are other colors.

These are simple one-celled organisms and are generally very tiny, although
Nostoc
, commonly called Mare's eggs, found in fresh water streams
can be as big as walnuts and may be the largest prokaryotic or bacterial-type
cells in the world. Their distinctive colors are due to accessory pigments
which assist the chlorophyll in light capture. The accessory pigments found
in cyanobacteria are unique to that group. In nature, cyanobacteria are common,
but typically not obviously dominant organisms. They are often characteristic
of polluted or highly organic environments. All single-celled algae are capable
of rapid growth, but the cyanobacters have the fastest growth rates. In optimal
culture, their populations can double every 20 minutes or so. They typically
secrete a mucoid layer around themselves, and when this, and the enclosed
cells, builds up to a visible thickness, we call it "red slime algae", as
the most common varieties in hobbyist tanks is a pinkish to red color.

In reef aquaria, a cyanobacter outbreak generally means an excess of nutrients,
primarily phosphates, nitrates, and dissolved organic material, generally
from over-feeding or some undiscovered mortality. Unfortunately, the cure
is not simple. Antibiotics can be used to kill the bacteria, but these don't
cure the underlying problem and some can have undesirable side effects, such
as significantly effecting the benficial bacteria do the biological filtration.
The most pragmatic solution seems to be to vacuum out as much of the slime
as possible and do a water change to lower the concentration of the nutrient
levels. This may have to be done several times in sequence over several weeks
to lower levels sufficiently to limit the growth of the bacteria. Additionally,
it may be necessary to cut back on feeding either in amount or in frequency.

DIATOMS
- the brown or golden slime on aquarium walls or substrata.
They generally put in the Kingdom
Protista
, and the Division
Bacillariophyceae
.

Diatoms also single-cell organisms but are significantly larger and more
complicated than cyanobacteria. They have cell walls containing silica. The
individual cells are yellow-green to brown. They contain two types of chlorophyll
and at some stage in their life cycles have motile stages which move by the
action of one or two tiny beating hairs called flagella.

Most diatoms show very limited mobility and exist primarily as groups of
cells growing a film over the surface of objects. In low concentrations they
probably don't have any noticeable effect in aquarium systems, and indeed
they are probably always present. Although they can respond to nutrient increases
in a manner similar to the cyanobacteria, they seem to be more responsive
to increases in the amount of dissolved silica in the water. Silicon, as
silicate, is dissolved in sea water, and these organisms use it to construct
their shells. Under normal conditions, diatoms can be generally well controlled
in aquaria by the use of grazers such as snails, or chitons, and by using
some sort of scraper to remove the film periodically from the walls.

If the aquarist has extra-high levels of silica and excess nutrients in the
water, then diatoms often "bloom" producing dense rapidly growing films which
can cover every exposed surface in the aquarium. Often the excess silica
seems to be caused by the use of river sand instead of calcareous sand, and
the cure is easy, but tedious, and that is the complete replacement of the
siliceous sand by calcareous sand. The use of silica-free deionized, distilled,
or reverse osmosis water can also help reduce problem outbreaks. The latter
cure will definitely assist in reducing the diatom population. It may have
the unintended result of also reducing or removing sponges and perhaps limpets
from the aquaria as these animals also require silica, and in relatively
high amounts, to live.

DINOFLAGELLATES
- the brown slime algae and zooxanthellae. They generally
put in the Kingdom
Protista
, and the Division
Dinoflagellata
or
Pyrrophtya
.

This group is characterized by having a rigid external skeleton or test made
of cellulose, and generally possessing two flagella which move them through
the water. They possess accessory pigments in addition to chlorophyll and
these pigments often give them a red or brown color. Some are also brilliantly
bioluminescent. Common in both fresh and salt water, dinoflagellates are
of immense economic importance, causing red tides and paralytic shellfish
poisoning. They are also immensely important for reef aquarists, as many
tropical invertebrates harbor these algae in their bodies.

The symbiosis of the invertebrate and algae provides both with benefit as
the algal cells get protection from environmental problems such as predators,
and the invertebrate gets nutrition from the alga. The algal symbiont also
gets some essential nutrients such as nitrogen from the animal. Reef-building
corals, clams in the genus Tridacna, many sea anemones, and some sponges
all harbor symbiotic dinoflagellates called zooxanthellae.

Dinoflagellates can also cause problems for an aquarist when they occur free
living in the aquarium. In a manner analogous to the other algae we have
discussed they can "bloom" to cause a brown slimy film that overgrows most
surfaces. It appears that this slime is also caused by too much nutrient
in the water, and as with the red slime, the cure is to lower nutrient levels
through the use of water changes and by siphoning out the slime.

Some dinoflagellates are not capable of photosynthesis and instead are either
predatory or parasitic. These seem to show up rarely in aquaria, and are
generally no cause for problems.

CHLOROPHYTA
- the green algae; contains hair algae,
Derbesia
species, some decorative algae, such as Caulerpa, and numerous
other forms.

Members of the green algae can be either single-celled or consist
of many cells. Except for some carotenoids, they generally lack accessory
pigments, and generally their color is a clear rich green. Many of them
incorporate calcium carbonate into their bodies. The multicellular chlorophytes
generally have a reproductive stage where they release thousands spores into
the water. These settle and produce new individuals elsewhere.

The unicellular green algae are very small, but important as food for many
suspension-feeding organisms. Most reef aquaria harbor an invisible population
of unicellular green algae that becomes noticeable only if their population
reach relatively high numbers, at that point they turn the water green.

Some pest algae are members of this group. These are the hair algae,
Derbesia
and similar species such as
Bryopsis
, and whorl algae
such as
Batophora
. These are common members of normal coral reef
communities. In natural systems, they are generally found in small patches
and are food for many common grazers. Many of these grazers are large fish
or large snails that unsuitable for aquaria. Consequently in our systems
these algae often have no biological controls such as herbivores, and they
can become very abundant nuisances that once established are very difficult
to control. Their control is basically the same as for the various slime
algae; remove as much of the alga as possible and reduce the nutrient, and
if possible, the light level. Occasionally some herbivores will eat them.
Abalone,
Haliotis
species, are often excellent controls for them.
Unfortunately the abalone can become too large for a normal aquarium. Most
grazing snails, while good for diatom, and dinoflagellate control, will not
eat the hair algae.

Valonia ventricosa
, the bubble alga, is also a chlorophyte.
This is a unicellular alga which grows fastened to the substrate. They can
range up to a couple of centimeters across. When few in number they can be
an attractive and interesting addition to a reef tank, but under certain
circumstances they can also bloom and they can over grow corals and other
invertebrates. They can be removed physically with forceps or some pliers.

Many
species of decorative algae are found in the
chlorophyta
. Perhaps
the most common are various species of Caulerpa. Other algae such as the
calcareous
Halimeda
,
Rhipocephalus
, and
Penicillus
species
are often grown as well. When a large individual of Caulerpa produces spores,
it can often produce enough to turn a large aquarium milky-green with them.
They either settle out, get filtered out, get eaten or die within a short
time, leaving the water clear again. The husk of the parent remains behind
as a mass of white flaccid tissue. It should be removed. All algae are leaky
and some varieties of Caulerpa have been implicated as producing chemicals
that have caused some animal deaths. In small amounts these algae are generally
benign, however.

RHODOPHYTA
- the red algae. These are multicellular algae
with very complicated life cycles often containing alternating stages with
morphologies that are very different from one another. They are only distantly
related to the other algae and appear to have little in common with them
other than the presence of chlorophyll. They have a reddish accessory pigment
that allows them to live deeper or under dimmer light conditions than other
algae.

The most common type of red algae found in aquaria
is crustose coralline algae. These appear as red, pink or lavender crusts
often with a white growing edge. Articulated forms are common in nature,
but relatively rare in marine aquaria. These are attractive organisms and
are generally desired in a reef system. Their presence generally indicates
satisfactory conditions for other organisms as well. Because of the presence
of alternate life stages and sexual and asexual forms coralline algae are
often damnably hard to identify to even genus.

Filamentous red algae can also be found in aquaria. They are often very abundant
in natural systems as well. These range from low-growing red fuzzes to larger
pink or red algal clumps. These are benign and attractive organisms and their
presence generally also implies a good population of small crustaceans which
often live on or around them.

PHAEOPHYTA
- the brown algae; contains rockweeds and kelps,
also some calcareous forms. These algae contain a brownish accessory pigment,
fucoxanthin, which gives them their characteristic brown color. Some species
of phaeophytes are the largest algae, and can be huge. Bull kelp,
Nereocystis luetkeana
from the U. S. West Coast can increase in length
at rates exceeding one meter per day, and the giant kelp off of California
can be hundreds of feet long.

With the exception of
Sargassum
species, brown algae are relatively
uncommon in marine aquaria. They are not particularly hard to culture, but
tend to prefer dimmer light situations then reef aquarists typically provide.
Often coralline algae can outcompete them for space in an aquarium. Most
brown algae are temperate organisms, and their tropical diversity is limited.
Occasionally species of the calcareous
Padina
are found in aquaria
where they can be very attractive.

OTHER ALGAE

There are numerous other algal groups, and some such as the coccolithophores
are exceedingly important in natural coral reefs; and indeed, in all the
world's oceans. However, most of these forms are either microscopic or rarely
seen in aquaria and I will not discuss them.